Roundup is a broad spectrum herbicide. That means it should kill any actively growing plant which absorbs the chemical. It is appealing to use during lawn renovations because re-seeding can occur within a short time after the chemical has been applied and it will not harm the germinating grass seedlings. If you see any areas that do not look as if they were killed by the first application, a second application would be recommended. RoundUp’s label instructions state to wait at least 3 days after application before seeding. Always read and follow the manufacturers label instructions when using any herbicide, pesticide or fertilizer.